[RFC PATCH v2 05/47] hugetlb: make hugetlb_vma_lock_alloc return its failure reason

[James Houghton]

Currently hugetlb_vma_lock_alloc doesn't return anything, as there is no
need: if it fails, PMD sharing won't be enabled. However, HGM requires
that the VMA lock exists, so we need to verify that
hugetlb_vma_lock_alloc actually succeeded. If hugetlb_vma_lock_alloc
fails, then we can pass that up to the caller that is attempting to
enable HGM.

Signed-off-by: James Houghton <jthoughton@xxxxxxxxxx>
---
 mm/hugetlb.c | 16 +++++++++-------
 1 file changed, 9 insertions(+), 7 deletions(-)

diff --git a/mm/hugetlb.c b/mm/hugetlb.c
index 52cec5b0789e..dc82256b89dd 100644
--- a/mm/hugetlb.c
+++ b/mm/hugetlb.c
@@ -92,7 +92,7 @@ struct mutex *hugetlb_fault_mutex_table ____cacheline_aligned_in_smp;
 /* Forward declaration */
 static int hugetlb_acct_memory(struct hstate *h, long delta);
 static void hugetlb_vma_lock_free(struct vm_area_struct *vma);
-static void hugetlb_vma_lock_alloc(struct vm_area_struct *vma);
+static int hugetlb_vma_lock_alloc(struct vm_area_struct *vma);
 static void __hugetlb_vma_unlock_write_free(struct vm_area_struct *vma);
 
 static inline bool subpool_is_free(struct hugepage_subpool *spool)
@@ -7001,17 +7001,17 @@ static void hugetlb_vma_lock_free(struct vm_area_struct *vma)
 	}
 }
 
-static void hugetlb_vma_lock_alloc(struct vm_area_struct *vma)
+static int hugetlb_vma_lock_alloc(struct vm_area_struct *vma)
 {
 	struct hugetlb_vma_lock *vma_lock;
 
 	/* Only establish in (flags) sharable vmas */
 	if (!vma || !(vma->vm_flags & VM_MAYSHARE))
-		return;
+		return -EINVAL;
 
-	/* Should never get here with non-NULL vm_private_data */
+	/* We've already allocated the lock. */
 	if (vma->vm_private_data)
-		return;
+		return 0;
 
 	vma_lock = kmalloc(sizeof(*vma_lock), GFP_KERNEL);
 	if (!vma_lock) {
@@ -7026,13 +7026,14 @@ static void hugetlb_vma_lock_alloc(struct vm_area_struct *vma)
 		 * allocation failure.
 		 */
 		pr_warn_once("HugeTLB: unable to allocate vma specific lock\n");
-		return;
+		return -ENOMEM;
 	}
 
 	kref_init(&vma_lock->refs);
 	init_rwsem(&vma_lock->rw_sema);
 	vma_lock->vma = vma;
 	vma->vm_private_data = vma_lock;
+	return 0;
 }
 
 /*
@@ -7160,8 +7161,9 @@ static void hugetlb_vma_lock_free(struct vm_area_struct *vma)
 {
 }
 
-static void hugetlb_vma_lock_alloc(struct vm_area_struct *vma)
+static int hugetlb_vma_lock_alloc(struct vm_area_struct *vma)
 {
+	return 0;
 }
 
 pte_t *huge_pmd_share(struct mm_struct *mm, struct vm_area_struct *vma,
-- 
2.38.0.135.g90850a2211-goog